These take precendence over the package registry where we have no control
on which entry will be used. The registry is only the last resort.
On some Linux version the most recently created package registry key will
be used. Please not that an entry is only created for a build try that is
not already in the registry. If there is already key, then not even the
modification date of the key will be updated. This default behaviour might
lead to strange mixes of build configurations.
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